The invention relates in general to bearings for supporting shafts for rotation and in particular to an improved structure for a center bearing assembly for rotatably supporting an intermediate portion of a vehicle drive train or coupling shaft assembly. More particularly, this invention relates in general to structures for damping vibrations in center bearing assemblies used in vehicle drive train assemblies.
In most rear wheel drive vehicles, a source of rotational energy, such as an internal combustion or diesel engine, is located near the front of the vehicle. The engine is connected by means of a drive train to rotate one or more driven wheels located near the rear of the vehicle. The drive train typically extends between a transmission, which is connected to the engine, and a differential, which is connected to the driven wheels. In some vehicles, the distance separating the transmission and the differential is relatively short. In these vehicles, the drive train includes a single drive tube, usually referred to as the drive shaft. In other vehicles, the distance separating the transmission and the differential is relatively long, making the use of a single drive shaft impractical. In these vehicles, the drive train includes a drive shaft and one or more coupling shafts. The coupling shafts are connected to the drive shaft (and to each other) by universal joints.
Drive trains that are composed of a drive shaft and one or more coupling shafts require the use of one or more intermediate resilient support structures, which are generally referred to as center bearing assemblies or shaft support bearing assemblies. A typical center bearing assembly includes an annular roller bearing within which the coupling shaft is rotatably supported. The roller bearing itself is disposed within a generally annular resilient support member. The resilient support member is, in turn, disposed within a relatively rigid, generally U-shaped bracket which is secured to a cross member extending between the side rails of the vehicle frame.
The resilient support member is provided to reduce vibrations of the drive train in the vicinity of the center bearing assembly and to prevent such vibrations from being transmitted to the vehicle frame. The resilient support member is typically formed from an elastomeric material, such as rubber. Under most vehicle operating conditions, known rubber support members are effective in substantially reducing the transmission of vibrations from the drive train to the vehicle frame. However, the vibration damping characteristics of such known support members, which depend upon the specific material and the particular configuration thereof, remain constant regardless of the vehicle operating conditions. Accordingly, the vibration damping characteristics of known support members can be optimized only for a single set of operating conditions. The vibrations generated by the drive train, on the other hand, constantly change with changes in the operating conditions of the vehicle. As a result, these support members may not provide optimum vibration damping of vibrations under varying operating conditions.
An additional problem associated with the vibration of center bearing assemblies, is that an undesirable audible noise is generated and subsequently transmitted to the driver of the vehicle and to the environment surrounding the vehicle. It is known that all mechanical bodies have a natural resonant frequency at which they tend to vibrate when operated at certain rotational speeds. This natural resonant frequency is an inherent characteristic of the mechanical body and is based upon many factors, including its composition, size, and shape. In the context of vehicular drive train assemblies, the engine and transmission assembly can sometimes generate vibrations that are transmitted to and accentuated by the drive train components when rotated. Also, the drive train components may be rotated at a velocity that is at or near their natural resonant frequency (or one or more of the harmonics thereof), causing vibrations to be induced therein. In either event, the vibrations generated in the drive train components may cause the generation of audible noise. Such noise is usually considered to be undesirable for obvious reasons.
Various attempts have been made to reduce the noise generated by vehicle drive trains during operation. Past attempts have been primarily focused on noise reduction for driveshaft tubes. Known noise reduction structures have been manufactured from many materials, including cardboard, foam, and the like. However, although known noise reduction structures are relatively simple and inexpensive in structure and installation, they have been found to have a relatively modest effect on the reduction of noise in some vehicle driveshaft tubes. Thus, it would be desirable to provide an improved structure for reducing the amount of vibration and noise that are generated in a vehicle drive train assembly during operation.
It would be beneficial if there could be developed an improved structure for a center bearing assembly which includes a mechanism for controlling the vibration characteristics of the center bearing assemblies. Such a mechanism would serve to dampen the vibration of the center bearing assemblies, and would result in a reduction in the undesirable noise that would be otherwise generated by that vibration.
This invention relates to an improved structure for reducing the amount of vibration and noise that are generated in a vehicle drive train assembly during operation. In particular, this invention relates to a piezo-based device that is attached or otherwise secured to a center bearing assembly in a vehicle drive train assembly for actively and passively reducing torsional and lateral vibrations that are generated therein during use. The piezo-based device is used to dampen these vibrations by converting the physical vibratory motion of the center bearing assembly into an electrical current that is dissipated through a resistive element as heat. By varying the magnitude of the resistive element, the center damping frequency of the piezo-based device can be varied as needed for the particular center bearing assembly and the drive train assembly as a whole. If desired, an inductive element may be provided in a circuit with the resistive element to dissipate the electrical current. The magnitude of the resistive element may be varied by a controller in response to the magnitude and/or frequency of the vibrations sensed by a sensor. Alternatively, the stiffness of the piezo-based device may be controlled by an electrical current generator that can be operated by a controller in response to the magnitude and/or frequency of the vibrations sensed by a sensor. The piezo-based device may be mounted at various locations on the center bearing assembly. If desired, a plurality of such piezo-based devices may be provided on the center bearing assembly.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.